1. Field of the Invention
The present invention relates to an electrodeposition painting system, and more particularly, to a closed system including a painting station and one or more rinsing stations, wherein the system includes a filtration. unit which provides paint rich components to the painting station and a solvent tank which is connected to the filtration unit and which provides solvent rich fractions to the rinsing stations. The invention is particularly characterized by the utilization of sensors in the solvent tank to generate signals which are used to control the operation of the system.
2. Description of Prior Art
Electrodeposition painting systems, particularly those used for applying a coat of paint onto the external and internal surfaces of an automobile body are known in the art. Examples of such systems are disclosed in Japanese Publication Nos. 57-194016, 57-207200 and 58-123,900. These systems are characterized by submerging an automobile body in an electrolytic bath and then rinsing the body through a series of rinsing stations. These systems are also characterized by the use of a filtration system which is capable of separating the paint contained in the electrolytic bath into paint rich components, typically, pigment, binder and a small amount of solvent, typically water, and solvent rich components, typically water. In use, the paint rich components which are separated in the filtration system are recycled back to the electrolytic tank and are used for painting an automobile body, and the solvent rich components are provided to the rinse stations and are used to rinse the painted automobile body to remove excess paint and solids from the paint which are stuck on the electrodeposited film.
The above painting systems have gained wide acceptance in the automobile industry. However, these systems suffer from a number of drawbacks. In use, the system operates continuously, with paint being continuously supplied to the filtration unit for separation into paint rich and solvent rich components. The continuous operation of the painting and filtration system results in increased operating costs, particularly at times when automobile body parts are not being painted. For example, the electrodeposited painting process may only be desired for one plane shift, amounting to approximately eight hours. Due to the continuous nature of the system, the filtration unit operates on a 24 hour cycle. Accordingly, unnecessary electrical and other operating costs are incurred as a result of the operation of the filtration system for 16 hours wherein automobile bodies are not being painted.
A further consequence of the filtration system operating on a continuous cycle is that if any of the elements of the system malfunction, the entire system is susceptible to accidental spillage of either water or paint. If such an accident should occur, cleanup costs and costs due to the inability to utilize the painting system will be incurred. Accordingly, the continuous operation of the filtration system poses a potential safety risk as a result of the system being unable to automatically shutdown in advance of accident.
In addition, the filters which are used to separate the paint into paint rich components and solvent rich components are susceptible to fouling by solids contained in the paint, feed. Such solids tend to accumulate throughout the system, and particularly in the filtration unit. If the accumulation of solids reaches a point wherein the filters. are completely clogged, the system has to be manually shut down and the filters have to be washed to remove the solid residue. Again, this results in an increase in cost as a result of cleaning, and production downtime.
Attempts have been made in the art to solve some of these problems, but a solution has not been proposed which can remedy all of the problems.
For example, Japanese Publication No. 61-227195 discloses a filtration device for use in connection with an elctrodeposition bath which is capable of intermittent operation according to the level of water maintained in a solvent holding tank attached to the filtration unit. Although the sensors maintained in the solvent holding tank function to start and stop the filtration unit, the publication does not disclose a solution to the clogging problem caused by the accumulation of paint residue throughout the filtration unit.
Accordingly, there exists a need in the art for an electrodeposition painting system including a filtration unit for separating paint into paint rich and solvent rich components wherein the system is capable of noncontinuous operation, and wherein the filters contained in the filtration unit may be cleaned during operation without incurring additional costs for system downtime.